A reference standard for urinary tract infection research: a multidisciplinary Delphi consensus study

The absence of a consensus-based reference standard for urinary tract infection (UTI) research adversely affects the internal and external validity of diagnostic and therapeutic studies. This omission hinders the accumulation of evidence for a disease that imposes a substantial burden on patients and society, particularly in an era of increasing antimicrobial resistance. We did a three-round Delphi study involving an international, multidisciplinary panel of UTI experts (n=46) and achieved a high degree of consensus (94%) on the final reference standard. New-onset dysuria, urinary frequency, and urinary urgency were considered major symptoms, and non-specific symptoms in older patients were not deemed indicative of UTI. The reference standard distinguishes between UTI with and without systemic involvement, abandoning the term complicated UTI. Moreover, different levels of pyuria were incorporated in the reference standard, encouraging quantification of pyuria in studies done in all health-care settings. The traditional bacteriuria threshold (105 colony-forming units per mL) was lowered to 104 colony-forming units per mL. This new reference standard can be used for UTI research across many patient populations and has the potential to increase homogeneity between studies.